Implicit Imitation of Regional Dialects in Typically Developing Adults and Adults with High-Functioning Autism

This study examined the effect of regional dialect on implicit spontaneous phonetic imitation in typically developing adults (TD) and adults with high functioning autism (HFA). Participants shadowed CVC target words produced by talkers from two American English dialect regions, the North and the Midland. Imitation was measured acoustically in terms of vowel quality, vowel duration, midpoint f0, f0 trajectory, and onset and coda consonant duration. It was hypothesized that TD shadowers would imitate familiar dialects less than unfamiliar dialects, based on previous results showing that high frequency words are imitated less than low frequency words (Goldinger, 1998). By extension, frequently encountered or familiar dialects should be imitated less than unfamiliar dialects. Effects of dialect familiarity were in the expected direction, with more imitation of unfamiliar dialects. TD shadowers also imitated perceptually salient targets, including those with long vowels, high f0, or rising f0. The TD productions and targets from the shadowing task were then used as stimulus materials in an AXB discrimination task to measure perceived imitation. Results suggest that TD shadowers were imitating some dialect features. Among the acoustic measures, perceived imitation was correlated with vowel duration and coda duration. HFA shadowers were expected to exhibit less imitation than TD shadowers based on research showing that impaired imitation is a characteristic of HFA (Stieglitz et al., 2008; Stone et al., 1990). This prediction was supported for vowel quality and onset duration, but HFA shadowers imitated vowel duration and midpoint f0 more than TD shadowers. HFA shadowers were less likely than TD shadowers to imitate perceptually long or high f0 vowels, but more likely to imitate long consonants. Effects of dialect familiarity for HFA shadowers were in the opposite direction from those for TD shadowers, with HFA shadowers imitating Northern targets less than the more familiar Midland targets. These results suggest an impaired ability for individuals with HFA in imitating unfamiliar or extreme phonetic variation.